1. Field of the Invention
The present invention relates to a scanning method. More particularly, the present invention relates to a single step multi-section exposure scanning method.
2. Description of Related Art
In general, a charge-coupled device (CCD) is used as the photosensitive element inside most color scanners. The color CCD is constructed using a large number of sensor cells each capable of sensing light intensity of one of the three primary colors including red (R), green (G) and blue (B). FIG. 1 is a schematic diagram of a conventional charge-coupled device (CCD). As shown in FIG. 1, the CCD includes a first row of sensor cells 102 and a second row of sensor cell 104 for detecting intensity of the primary color red (R), a third row of sensor cells 106 and a fourth row of sensor cells 108 for detecting intensity of the primary color green (G) and a fifth row of sensor cells 110 and a sixth row of sensor cell 112 for detecting intensity of the primary color (B). After a period of exposure, each sensor cell accumulates a definite amount of electric charges according to the intensity of light falling on the particular sensor cell.
FIG. 2 is a schematic diagram showing a conventional scanning circuit of a scanner. As shown in FIG. 2, a sensor 202 converts the electric charges accumulated inside the CCD (not shown) into an analogue voltage signal. Through an analogue/digital converter 204, the analogue voltage signal is converted to a digital voltage signal. Thereafter, an application specific integrated circuit 206 initiates a computation of the compensation value supplied from a compensation RAM unit 210 and the digital voltage signal. The computed video signal is transferred to a video RAM unit 208 for storage. In a subsequent step, the application specific integrated circuit 206 reads out video signal data from the video RAM unit 208 and transmits the video signal data to an input/output port 212.
Resolution of a scanner is an important parameter for judging the quality of a scanner. However, the production of a high-resolution scanner often causes some critical problems including: (1) lamp-adjusting techniques have to be deployed to resolve sensor saturation problem because long exposure will lead to saturation of the CCD while short exposure will lead to insufficient time for outputting voltage signal; (2) using a run-stop-scan scanning method to scan a document not only leads a repetition of start, rotate and stop motion for the stepper motor, but also leads to a slow down of scanning speed; (3) the CCD generates a large quantity of voltage signal data so that storage capacity of the compensation memory has to increase, thereby restricting large area scanning for obtaining a higher resolution; (4) the generation of large quantity of voltage signal data by the CCD also necessarily increases the storage capacity of the video RAM unit.